1. Field of the Invention
The present invention relates to a process of producing 2-(5-ethyl-5-hydroxymethyl-1,3-dioxane-2-yl)-2-methylpropane-1-ol (hereinafter referred to as “dioxane glycol” or “DOG”), which is represented by the following formula I:

2. Description of the Prior Art
DOG is produced, for example, by a process including the acetalization of hydroxypivalaldehyde (hereinafter referred to as “HPA”) represented by the following formula II:
with trimethylolpropane (hereinafter referred to as “TMP”) represented by the following formula III:
in the presence of an acid catalyst; and the filtration, washing and drying of DOG crystals precipitated in the reaction product liquid (JP 62-59104B).
The particle size of DOG crystals produced by the process of JP 62-59104B is as extremely small as 10 μm or less. Therefore, the solid-liquid separation after the reaction takes a long time, to reduce the efficiency of the solid-liquid separation. In addition, since the wet cake obtained by the solid-liquid separation has a high liquid content, a long time is required for drying, to reduce the efficiency of drying. DOG having a small particle size is easy to form dust, to make the handling thereof difficult. Additionally, since DOG having a small particle size which has been produced by known methods is electrostatically charged quite easily, there is a strong possibility of dust explosion.
However, the documents describing known production methods are completely silent about the increase in the particle size of DOG, and therefore, it has been desired to develop a process of producing DOG having a larger particle size. The particle size of DOG crystals produced by known methods can be increased by a purification such as recrystallization. Such measure is, however, industrially disadvantageous, because not only additional chemicals, apparatuses, etc. are required, but also the number of steps for the production of DOG is increased.
DOG has the following two isomers: trans isomer and cis isomer.
DOG or its derivative composed of a mixture of the trans isomer and cis isomer is not suitable as the raw material for industrial use, because products having poor properties are produced. Therefore, DOG is required to have a high content of the trans isomer (hereinafter referred to as “high trans-isomer purity” or merely “high purity”).
However, the documents describing known production methods are completely silent about the isomer purity of DOG. As a result of extensive studies by the inventors, it has been found that DOG produced by known methods has a low trans-isomer purity, although mainly composed of the trans isomer. For example, the highest melting point of DOGs actually disclosed in the working examples of JP 62-59104B is 121.5° C. However, a purified DOG having a trans-isomer purity of 99% or more, which is obtained by the recrystallization from acetone of DOG having such highest melting point, shows a melting point of 125° C. or higher.
As described above, although the purity of DOG produced by known methods can be increased by purification such as recrystallization, such measure is industrially disadvantageous, because not only additional chemicals, apparatuses, etc. are required, but also the number of steps for the production of DOG is increased.